Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA, USA
Metomidate hydrochloride is an imidazole-based, non-barbiturate hypnotic drug primarily used as an immersion sedation and anesthetic agent in freshwater and marine finfish.1-3 To the author’s knowledge, there is no documentation in the literature of its use in amphibians. In this study, seven male and four female leopard frogs (Rana pipiens) were induced with metomidate (Metomidate hydrochloride powder, Western Chemical, Inc., Ferndale, WA, USA) via immersion bath at a concentration of 30 mg/L for 60 min. The pH of the induction solution ranged from 7.63 to 7.75. Each frog was then removed from the induction solution, rinsed, and recovered in 80°F (26.6°C) amphibian ringer’s solution.4 After 210 min in the ringer solution, the frogs were transferred to moist paper towels for recovery. Heart rate, gular and abdominal respiration rates, righting reflex, superficial and deep pain withdrawal reflexes, corneal and palpebral reflexes, and escape response were monitored and recorded at defined intervals during both induction and recovery. The average time to loss of righting reflex and escape response was 17.36 min and 17.82 min, respectively. Metomidate produced clinical sedation in all frogs (n=11). Surgical anesthesia was achieved in only 27% (3/11), with an anesthetic duration ranging from 9 to 20 min. Recovery times were extremely prolonged and varied, with a range from 313 min to greater than 600 min. Our findings suggest that metomidate hydrochloride is unsuitable as a sole anesthetic agent in leopard frogs, and further research is needed to evaluate its suitability in other amphibians.
The authors thank Dr. John Hawke and Judy Wiles with the Department of Pathobiological Sciences, Louisiana State University School of Veterinary Medicine, for their knowledge and expert technical advice.
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2. Kilgore, K.H., J.E. Hill, J.F.F. Powell, C.A. Watson, and R.P.E. Yanong. 2009. Investigational use of metomidate hydrochloride as a shipping additive for two ornamental fishes. J. Aquat. Anim. Health 21: 133–139.
3. Small, B.C. 2003. Anesthetic efficacy of metomidate and comparison of plasma cortisol responses to tricaine methanesulfonate, quinaldine and clove oil anesthetized channel catfish Ictalurus punctatus. Aquaculture 218: 177–185.
4. Wright, K.M., and B.R. Whitaker. 2001. Pharmacotherapeutics. In: Wright, K.M., and B.R. Whitaker (eds.). Amphibian Medicine and Captive Husbandry. Krieger Publishing Company, Malabar, Florida. Pp. 309–330.